A heat treatment device is known that comprises an enclosure with means for conveying the substance between the inlet of the enclosure and the outlet of the enclosure, which means comprise a screw mounted to rotate inside the enclosure about an axis of rotation and means for driving the screw in rotation. The device also includes means for heating the screw by the Joule effect.
The substance for treatment is usually inserted into the inlet of the enclosure in the form of divided solids. The screw urges the particles of substance continuously towards the outlet of the enclosure. Because of the temperature of the screw, the substance is heated progressively as it advances, thereby subjecting it to heat treatment (drying, debacterization, cooking, roasting, pyrolysis, . . . ).
Such a device enables the treated substances to be heated uniformly.
Nevertheless, because the conveyor means do not have a shaft around which the screw winds, the screw rests against the inside wall of the enclosure. However, the enclosure is generally made of metal and is thus electrically conductive. In order to avoid a short circuit in the device when the means for heating the screw are active, the inside wall of the enclosure is thus covered in a layer of electrically insulating material against which the screw comes to bear directly.
Nevertheless, the screw rubs against the electrically insulating layer as it rotates inside the enclosure, thereby tending to damage the layer. Such a layer turns out to be difficult and expensive to replace.